A fourth man - a citizen of United Arab Emirates - is accused of supporting the men in carrying out surveillance on a host of potential targets prior to the co-ordinated attacks, which left about 3,000 people dead.

According to the memo quoted by The Telegraph, the three Qatari citizens carried out surveillance at the World Trade Center, the Statue of Liberty, the White House and in Virginia, the state where Pentagon and CIA headquarters are located.

The cable says the men flew into New York from London three weeks before September 11, 2001.

Ten days later, they flew to Los Angeles and checked into a hotel close to the airport. They were to check out on September 10 and were booked on an American Airlines flight from Los Angeles to Washington, but failed to board the flight.

The following day, the same aircraft, flying on route AA77, was hijacked and crashed into the Pentagon.

The three suspects reportedly flew back to London before returning to Qatar. Their present location is unknown.

'Suspicious activity'

The Telegraph quotes the memo as saying that staff at the Los Angeles hotel had grown suspicious of the men.

Raising their suspicion was the men's refusal to let them clean their room during the last days of their stay.

The staff had also noticed pilot type uniforms, several laptops and several cardboard boxes addressed to Syria, Jerusalem, Afghanistan and Jordan in their room in previous cleaning visits.

According to the memo, sent by the US embassy in Doha to the department of homeland security, and quoted by the paper, "the men had a smashed cellular phone in the room and a cellular phone attached by wire to a computer. The room also contained pin feed computer paper print outs and headers listing pilot names, flight numbers, and flight times".

The memo recommended that the men be put on a "no-fly" list.

The September 11 attacks have been the worst on US soil to date. Only one person - Zacarias Moussaoui - has been tried and convicted over the attacks.

Details of other plotters have never been previously disclosed.

The three Qatari men were included on a FBI list of more than 300 people who were sought for questioning in connection with the attacks. The list was leaked in 2002.